Advanced Materials Research Vols. 941-944

Abstract: Molecular dynamics simulation has been performed to explore the structural and dynamical properties of undercooled Cu50Co50 melt based upon the embedded atom method (EAM), namely due to Zhou. With the reduction of temperature, liquid phase separation phenomenon is more obvious. The simulated coordination number (CN) of liquid Cu50Co50 indicate that no stronger interaction of heterogenic atom pairs than those of the same atom pairs happens in melts, and Cu50Co50 melt is close to an weak demixing system. And the Bhatia-Thornton (B-T) structure factor gets the same result. Temperature dependence of mean squared displacement (MSD) shows very weak glass formation behavior of Cu50Co50. Our work discusses that the relationship between the properties and L-L phase separation in undercooled liquid of Cu50Co50.

Abstract: The effect of mixed RE elements (Y, Nd, Gd ) on the microstructure and tensile properties of die-cast AZ91D alloy were investigated. The results indicated that the content of mixed RE elements lead to the change of the formation of Al_▔RE compounds and reduction of the fraction of β-Mg₁₇Al₁₂ phase. The grain size of the alloy added 1.0wt. % RE became smaller than die-cast AZ91D and AZ91D+2.0wt. % RE alloys. The UTS of die-cast AZ91D+xRE(x=0 wt. %, 1.0wt. %, 2.0 wt. %) alloys were 204MPa, 194MPa, 203.6MPa at room temperature, respectively. Moreover, RE addition resulted in fracture behaviors changed.

Abstract: Cast aluminium alloy 354 has become an important industrial material owing to its excellent mechanical properties and good castability. It finds widespread use in the manufacture of compressor wheel castings. Castings have been studied since long and different approaches have been attempted to improve their quality. One such approach is Hot Iso-static Pressing (Hipping). This paper studies the effect of Hipping on the strength, ductility, strain energy density W and quality rating Q_o of the alloy 354. The study shows that Hipped samples have better % elongation to fracture, higher W and Q_o values as compared to non-Hipped samples. This behavior is consistent across different aging conditions of the alloy. Hipping also results in a reduction in scatter of ultimate tensile strength of 354, thus making it valuable to industries that demand high material consistency.

Abstract: In order to develop new Al alloy, the quasi-static and dynamic compression deformation behavior of an advanced Al-Mg alloy, which contained Zn and rare earth, were investigated. Deformed microstructures in the shear bands of this alloy were characterized by optical microscope. Results show that the compressive strengths increase with strain and strain rates being increased, and microstructures of deformed Al-Mg alloy along compression directions are sensitive to strain rates. The distorted deformation twins near the deformed band can be formed under low strain rate of 5.6×10^-3 s^-1, while multiple shear bands slipping can be induced by dynamic deformation under high strain rates from 1.9×10³ s^-1 to 5×10³ s^-1. Therefore, compressive strength and fracture strain of dynamic deformation are higher than that of the quasi-static deformation, which is attributed to the strain hardening and grain refining in the multiple shear bands.

Abstract: 357-T6 is an alloy that has been widely used due to excellent casting properties and mechanical performances. The aluminum wheels can be cast with both permanent and low pressure die castings. In this study, the mechanical properties of 357-T6 were compared between the gravity permanent casting (GPC) and low pressure die casting (LPDC). The specimens were cast through permanent and LPDC processes, respectively and were heat treated under T6, with different aging temperatures 155°C, 165°C, 175°C and 185°C after the solution treatment of 545°C for 9 hours. The ultimate tensile strength and elongation were tested for both processes. The results show that both tensile and elongation of low pressure die casting specimens are higher remarkably than those in gravity permanent casting. The optimized aging parameter is heating at 175°C for 4.5 hours after solution treatment.

Abstract: The diffusion bonding process of commercially pure titanium to Q235B is achieved using copper as interlayer. The microstructure, component distribution and phase formation at the interface is analyzed by the use of microscope, SEM and XRD, the mechanical property is also investigated through the shear test. There is a good bond at the interface from 900 to 1000°C, no big cracks and voids, Q235B/Cu interface is straight, and Cu/TA1 interface shows waviness. With the increase of diffusion temperature from 900 to 1000°C, the shear strength increases first ,and then drops, however, with the increase of holding time from 30 to 60 minutes, the shear strength drops all the time, the maximum shear strength is 80MPa at 950°C for holding time of 30 minutes.

Abstract: A356 is a heat treatable cast alloy which has been widely applied in aviation and automobile industries. In this paper a Sb modified A356 alloy cast with permanent mold has been investigated in order to improve its mechanical properties by changing the needle morphology of the eutectic silicon. The results show that a small amount of Sb addition can contribute refined eutectic silicon morphology and enhance the mechanical properties, especially elongation of the A356 cast alloy poured in permanent molds. The optimal addition of Sb is 0.2 wt.%.

Abstract: In this research, one solid state processing technique, friction stir processing, is applied to modify the AZ61 magnesium alloy billet. The FSP modified AZ61 alloy could be refined to 3-8 μm via the dynamic recrystallization during processing. The AZ61 magnesium alloy billet with 75μm grain size could be refined to about 7.5μm by four-pass friction stir processing. The hardness of the stirred zone could increase to around 70-80 after friction stir processing, and after a further compressive strain of about 3% could raise the hardness to 81. The ductility of the weld direction specimens of the modified alloy could have a 235% elongation at 300°C and 1x10^-4 s^-1. The grain boundary sliding (GBS) might be the dominant deformation mechanism during superplastic deformation.

Abstract: An online production technique was designed and automated for control system of the three-phase induction motor based on programmable logic controller (PLC) technology and a simplified system was used to carry out a material testing. The microstructure morphologies were observed by the optical microscopy and hardness test. The results have shown that electric pulse treatment significantly accelerated the recrystalliazation annealing of HSi65-1.5 alloy due to the short treating time, high heating rate and accelerated nucleation and lower final dislocation density and the optimum parameters where found to be annealing at 300°C, pulse voltage of 700V, pulse frequency of 15Hz and pulse time of 120s.

Abstract: The wetting behavior of molten Cu-Ti alloys with titanium content of 10mass%, 20mass% and 30mass% on the Yttria Partially-Stabilized Zirconia (Y-PSZ) substrates was investigated at 1273K using the sessile drop method. The wettability improved with increasing the titanium content of the alloy. The stabilized contact angles of Cu-10mass%Ti, Cu-20mass%Ti and Cu-30mass%Ti alloys on the Y-PSZ substrate were measured to be 69°, 47°and 30°, respectively. The surface tension of the molten Cu-Ti alloys and the work of adhesion of alloy/substrate interface increased with increasing the titanium content. A larger work of adhesion attributes to firmer bonding between the molten Cu-Ti alloy and the Y-PSZ substrate, and can greatly improve the wettability.